Our PADI Tec Rec Gas Blender Course

Here at Master Divers we are incredibly proud to be running our popular Tec Rec Gas Blender course on monthly basis! With the same guaranteed ratio of 4 students to each instructor that we offer on all of our courses, we provide both student and instructor levels of training.


The popularity of technical dive courses is growing fast, and more people are diving with Enriched Air Nitrox than ever before. In fact, the PADI Enriched Air Diver course is now the most popular specialty on the market.  This means in turn that the demand for enriched air tank fills is also increasing. However, there needs to be someone qualified on hand to fill the tanks needed to meet demand. This is where the PADI Gas Blender course comes in…

TecRec Gas Blender Manual


The Tec Rec Gas Blender course will help you stand out on your CV, setting you apart from other Divemasters, Instructors and MSDT’s, and making yourself more employable! Having Gas Blenders on staff is important for all schools offering Enriched Air Nitrox to their customers. Aside from being a valuable asset to dive operators here on Koh Tao, it is also a required qualification for many staff working in more remote locations elsewhere, and on Live-aboard vessels too. Plus, as well as the standard PADI curriculum, we’ll teach you how to operate a compressor in terms of basic maintenance and procedures – something that all dive professionals should know something about!

Enriched AIr Nitrox (Eanx)
Enriched AIr Nitrox (Eanx)



The Tec Rec Gas Blender course will train you as a qualified Gas Blender, allowing you to provide gas mixes to all appropriately certified consumers. You’ll learn more about the physical properties of oxygen, its associated hazards, handling requirements and what cleaning equipment is necessary. Finally, you will learn the five methods of obtaining the desired enriched air nitrox mix, the advantages and disadvantages of each, as well as the various methods used to obtain proper helium mixes.

It is a very hands on course but as with all of our programmes, there is a little self-study to complete beforehand! The Tec Rec Gas Blender Manual is included in the course cost, so between this and your instructor, we will familiarize you with the all of procedures and techniques needed to get you out there as a fully qualified Gas Blender on completion of your course (certification fees are also included in the price).



You must be at least 18 years of age and a PADI Enriched Air Diver certification (or qualifying certification from another organization) to enrol.

The student level course costs 10,000THB, and is inclusive of all teaching materials, instruction, practice time and certification costs. If you’d like more info on becoming a Tec Rec Gas Blending Instructor, please contact us for more details.

The course runs over 2 days, and we do try to schedule it so it fits in best with the lives of working professionals. So typically the course will begin on full moon party day each month, and complete the day after, meaning you won’t need to miss out on group bookings for guiding or teaching. But as with any course, we can be a little flexible based on your requirements, so just let us know what works for you and we’ll try our very best to meet your needs!

So…what are you waiting for? Email, call or just pop in to book your Tec Rec Gas Blender course today!

Underwater Communication

Effective communication underwater is crucial throughout a dive to keep a dive group together and to ensure everyone is safe, comfortable and still has plenty of air. Dive leaders will communicate their instructions and intentions to other divers, and will often point out and name many marine life species to a dive group so that everyone knows what amazing creatures they are seeing. However, for obvious reasons communication underwater has to be slightly adapted to communication on land. Firstly, we are unable to speak whilst diving because of our regulator and the limited frequency and amplitude of our voices. Another problem is that water actually increases the transmission of acoustic sound due to its density and elasticity meaning sound waves hit both our ear drums at such a speed, the time difference between right and left (or vice versa) is too small for our brains to determine its direction.

Therefore, the easiest and simplest way to communicate whilst diving is by using hand signals. These are easily learnt and understood within the diving community to convey essential messages whilst underwater. From okay, to not okay, asking and responding to air, instructions to ascend or descent, these can immediately be both sent and received at the flick of the wrist. Most dive professionals will also have home grown signals specific to their style and environment, so keep an eye out and listen to the dive briefing on every dive!


Hand signals are adequate for diving, as good buddies and dive groups stay within visual distance of each other, are attentive to others actions, and are recreationally in very safe conditions. However, how can underwater communication be more effective and improved, and what new technologies are being developed?

Our main source of land-based communication is through radio waves, water prevents the propagation and transmission of radio waves unless at very low frequencies, which then limits the power of data transmission and communication. Submarines can use extremely low-frequency radio waves at shallow depths to receive communication (but not transmit), however this is not very applicable to divers who wish to communicate to one another on a dive. To develop more effective underwater communications systems, science looked to nature and found that by harnessing the use of acoustic sound waves as whales and dolphins do, we can begin to send and receive data over greater distances and to greater depths. Special communication systems called hydrophones have now been developed that have the power to convert speech into an ultrasound wave that is emitted in high-frequency vibrations too acute for the human ear. These ultrasounds travel through the water very effectively and are detected and decoded by another diver’s receiver which converts it back into sound. This system clearly has many benefits for recreational divers in buddy teams, but even more so for high-risk tech diving and commercial diving where divers are able to communicate clearly with both each other and any surface support


This technology is great for safety, and there are already products in development to allow simplistic communication through buddy devices that don’t rely on voice communications. So although many divers may not feel the need for open voice communication channels underwater, an additional ‘buddy bracelet’ may become common in recreational diving in the future and allow instant communication at the touch of a button. As the technology advances further, researchers hope to make vast improvements to tsunami detection, pollution monitoring and offshore oil and natural gas exploration.

DART II System Schematic


Voodoo Gas, Blend it Baby!

Voodoo Gas, Nitrox, or to give it the correct name, Enriched Air Nitrox (EANx) is still a mystery to some people. Why use it, why pay for the course to learn how to use it, and what are the benefits? I found out the answers to these questions many years ago when I did my PADI EANx Course. Back then it wasn’t that common, hence the nickname ‘Voodoo Gas’.

Nitrox Tank

For the uninitiated, EANx is used by divers in order to have longer dives at certain depths due to the fact that the percentage of oxygen is increased. This means that the percentage of Nitrogen is decreased, nitrogen being the limiting factor in depths and times of dives. Normal air is 21% oxygen and 79% nitrogen, whereas the two most common blends of EANx are 32% or 36% oxygen leaving only 68% and 64% nitrogen respectively.

One of my biggest questions, however, remained unanswered – ‘How do we get Nitrox into our tanks?’ – I had a rough idea but it wasn’t until I recently undertook my PADI TecRec Gas Blending Course that this was fully answered!

For the first time in a while the instructor became the student as I was handed my Gas Blending Manual and told to complete Knowledge Reviews 1,2 and 3….now don’t get me wrong but I am used to being the person asking students to give up their evenings to study, now I am being asked! Oh well, for the greater good…

The next morning I met up with Wilco, who was to be my instructor for the next couple of days, and we walked through the reviews, adding ‘meat to the bones’ where we needed so I had a full understanding of how EANx is blended and the possible hazards of the differing procedures and how we avoid them.

Next it was onto the practical side of things and actually learning to fill a cylinder with nitrox rather than normal air. Knees knocking, I followed Wilco to the compressor room and started to learn all about all the workings of the complressor and how to blend different mixtures of gases correctly – but only after a stark warning from Wilco – ‘When filling nitrox, please don’t blow up the compressor room!’ – now I am not usually a nervous individual but that got the sweat trickling down my neck, or was that the 38 degree heat?

Gary Blending Nitrox

So we worked step by step through everything from attaching the tanks to the filling whips (the hoses used to put the Nitrox into the cylinder), to startup steps for the compressor, to how we add the oxygen to the normal air to achieve the desired percentage blend and finally to the full shutdown upon the fill of all the cylinders needed.

Ten cylinders later I felt comfortable in blending Nitrox, as long as I followed Wilco’s expertly written step-by-step guide! I went on to complete the rest of the Knowledge Reviews and take the final exam…scored an 88%…not too shabby!

I have been regularly blending and filling our Nitrox cylinders since my course and am getting more comfortable each and every time. I may even be able to ditch the step-by-step guide sometime soon!

For anyone who hasn’t got their PADI Nitrox Certification yet I highly advise doing it, maybe in conjunction with your PADI Advanced Open Water Course and that way, you too can experience ‘Voodoo Gas’ on your next dives!

Trying technical diving ….

Every professional candidate at Master Divers gets to take the tech gear out for a spin.  As part of their internship they get to experience many other aspects of the diving world and throwing on the tech gear and understanding a little about the set up and how it differs is part of this.  This program is actually called Discover Tech and is included free of charge.

Without fail everyone returns from the trip having thoroughly enjoyed the experience and having learned something new – which is the aim after all.    Some do decide to learn more and take their Tec 40 while others are just happy to have achieved something different.    Today it was the turn of Dave, Tracey and Dan.  They all practiced some skills and techniques that are different from using a recreational set up.








Everyone also got the chance to have a swim and see how their buoyancy and trim was effected by the different gear and its weight too.  We also gave them the opportunity to have a go at sending up a lift bag.  This is all completed in shallow water – for some simple practice and experience.  One of our newly qualified Dive Masters went out with them to photograph today too – so thanks to Caz for these lovely photographs and well done to Dave, Tracey and Dan !

Discover Technical Diving

After completing a Tec 40 and with the tech kit still wet – we thought it would be a great idea to let some of our professional candidates loose with the gear.

We do this with all of our candidates, we think its great for their learning and understanding, even if they would never consider taking technical courses for themselves.  What we do is like a recreational Discover Scuba Dive and called Discover Technical Diving.It essentially gives an overview of the equipment and we explain why you might need it all and why there is so much of it.  Some techniques are different too and we give you the chance to have a go and practice.Actually diving around is different too so we make sure theres plenty of time for that – and looking cool for the camera too.If you want to find out more and have a go too – get intouch and we can advise you the best thing for you.

The MV Trident after 18 months underwater.

The MV Trident holds a very special place in my life, I spent lots of time aboard, on tech liveaboards diving deep ship wrecks located in the Gulf of Thailand and have many memories attached to both my time onboard and underwater.  It gave rise to the first few articles I had published and certainly fed my thirst for wrecks.

It was synonymous with Master Divers for many years and many here have fond memories of the time when Master Divers was its base.  Its owner, Jamie Macleod, is arguably our scuba-diving-dad.  He taught Elaine many courses throughout her career and taught and inspired Wilco and I technical training too.

The vessel plied the waters of the Gulf and a bit beyond locating wrecks that had long been lost and forgotten and played a big role in writing the history of wreck diving in this area. The atmosphere onboard when looking for a new wreck was great, the anticipation and just the slightest chance to dive where no else had was exciting. The most famous wreck she found was the USS Lagarto, a WWII submarine which lies fully intact on the ocean floor in 72m of warm clear water.  I wasn’t onboard for that find but dived the sub quite a few times and wrote about her for The Undersea Journal,  Diver UK, Scuba Diver Australasia and my photographs featured in Dives 100 Essential Wreck Dives.  There are many more amazing wrecks out there that are rarely dived and the feeling of privilege with a side portion of smugness was always apparent.






She had certainly done her hard yards and in September of 2010, after being stripped and made safe, she was allowed to sink to become an artificial reef off the south end of Koh Tao.  It seemed fitting that THE wreck hunter become a wreck herself.  She sank quickly to the depths and rested on her side in about 35m of water. At this point she was the only wreck on Koh Tao in recreational depths preceding the HTMS Sattakut.












The depth was planned to offer a great training ground for entry level tech as well as the deeper dive on the Deep Dive course.  She offers something different for the more experienced diver and always gives our gas blenders something different to mix the the usual 32% or 36% EANx too.

The last time I dived her was Jan 2011 so I was eager to see how she was doing and bring some pictures back too.  She can be a bit more of a challenging dive, due to her depth but also due to her location in what can be quite a current-y area.  We time our dives on her for the tides and have mostly hit it right.  Today was no exception – just a mere whisper of current which picked up a little by the time the techies arrived at their deco.

As you will see from the photographs, the viz wasnt great, but I have done my best to bring back some images to show how she is now.

Arriving at the bow the first thing I noticed was the logo was missing, completely gone from what you can see above.  You can see the odd patches of blue paint but nothing more.












The wheelhouse is one of the few pictures that I have from before and you can easily see the difference in growth…



The ceiling in the captains cabin / wheelhouse has fallen in trapping the lines laid by previous divers.  This is where I used to stand on my tiptoes straining to see the depth sounder as we slowly passed over an area where a wreck might be looking for anomalies on the bottom.

The saloon, which was mostly referred to as ‘the aircon room’, was a base for charging batteries, fixing kit and chilling infront of the TV after a hard days diving.  It certainly was not for ‘wet people’ but often a place to hide ‘goodies’ that you didn’t want others to eat!  The upper deck was lined with benches at the rear, a place to both watch and tease those on the deco station below and a general good vantage point, a great sunset spot and often the male changing area ; it being hidden behind the wetsuit rail ……being (usually) the only female on the boat certainly came with its challenges !

The stairs were a hive of activity at diving times and food times and a certain challenge if you were tall and in a rush but if you were small and/or daring you could swing yourself to the dive deck below – landing with a bang next to the oxygen tanks and filling station!  The camera bucket was tied here too and along with the benches the stair rails were pressed into service as drying racks on the return journey.  What Jamie would always refer to as a technical diving jumble sale !

There’s one of these horseshoe shaped seating areas on each side of the upper deck.  Heavy circular tables used to sit in the middle, providing places to plan dives, perch your laptop and ofcourse eat!


The back platform of the dive deck is where, I at least, would wobble in full kit slowly shuffling to take a giant stride into the deep blue.  This is also where a line would be dropped where you could attach your spare tanks once on deco.  Yes – I managed to drop one once and unsecured it made its way to the bottom but it was later recovered (phew)!



















Lights and flags were mounted here, but the top rails which were the framework for the shade has collapsed and lies on the deck too. The dinner bell hung here too and woe-betide you if you even so much as dared smell the food before the bell was rung!   As I returned back to the bow and the line, I took a quick snap of the wheelhouse from the front.  You can see the lines laid that go through the now inaccessible wheelhouse. 

The dive was fun, it was certainly interesting to see her after so much time and see how the life had moved in.  There was plenty of fish and a monster barracuda and grouper lurking around too.  It was certainly curious to swim around a wreck I knew as a boat so well and a different experience to a wreck whose history you know second hand.  Hopefully I’ll get back quicker next time !



Did you dive from the MV Trident ?  Feel free to share your memories in the comment box below ………..



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DMTS and MSDT try the tech kit for size !

Master Divers has always enjoyed a bit of tech and have had a long standing relationship with the tech liveaboard team based on Koh Tao.


We think its a great part of any divers learning but know that its not for everyone.  So we offer something in the middle.  We offer what is essentially a try dive in tech kit and all our MSDTs and DMTs get this as a free extra as part of their course.It is optional but most do opt to do it.  We explain the workings of the rig and how its different and why.  This is the part that’s great for learning, so atleast the have a simple understanding of a tech rig.  Then we take it out for a very shallow spin so that everyone can get a feel for it.  Last time we took a video and you can see the guys having a go at some of the skills and techniques that are different to a standard recreational set up.  Everyone thoroughly enjoyed the afternoon and a couple are considering completing the Tech 40 course.  You can see all the photographs from the day below……


If you want a first person account of what the afternoon can be like and a veritable female perspective then check out Rachaels great (hilarious)  blog about her experience with twin tanks!


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The History of Shipwreck Diving on Koh Tao, Thailand.

Wrecks have always been a passion of mine, I learnt to dive in South Africa where there are many and I loved the somewhat spookiness of them.  The way they materialize from the depths  as you descend and their histories and stories make for a more enriched dive – well that’s my point of view anyway.  I came to Koh Tao passing through maybe around 9 years ago, made a few dives and then returned a couple of years later to take my Dive Master and Instructor qualifications.   I loved the diving and the lifestyle here but the only thing missing for me were wrecks.

After traveling and teaching and diving all over the world, I returned to Koh Tao some years later to find a bunch of wreck divers had got off their neoprene clad bottoms and gone to see if they could find something a little more tantalizing.  They were all technical divers who created their own niche simply to ensure that they could keep searching for and diving on wrecks. Their home and base was Master Divers and really how I first encountered the shop that I’m now a partner in.

By the time I had met them they had scored the wonder goal in terms of wreck diving and found the USS Lagarto a WWII Submarine – not bad eh?  I wanted in, but I certainly needed more training first so Tech Deep was next.  On this course one of the wrecks  I visited was the Unicorn which was, at that time, the closest wreck to Koh Tao – just an hour away.   (The closest unless you counted a tuk tuk or a small catamaran.  To be fair the catamaran has lots of life on it and but hardly merits more than 10 mins of  exploration on the dive around the coastline) Although you can dive this at 40m, and a few more experienced divers do go along for a day trip for something more challenging, it was more used for technical training and experience dives for the Tec 50 course.   It certainly makes for an interesting dive, the bow is a strange and confusing affair when you find it and there’s a monster jew fish that stalks the wreck too.  He always made me jump.   Over the years its been interesting to see this wreck slip and lean steadily into the sand proving that the salt water wrecks that we dive now will be just a memory by the time our grand-kids are diving – toting the latest in CCR technology no doubt.So now fully trained I really wanted to jump on one of the liveaboard trips and check out some of the wrecks I had been hearing about.

The HTMS Phangan is a great wreck to cut your teeth on. She was a Thai Navy vessel built by the Japanese before WWII.  She’s around  60m in length and approximately 3000 tons.  She lies on her port side in 60 metres of clear water, the top of the wreck is at 48m.

She was allegedly overcome by big waves but there is evidence of fire damage everywhere and given that she was carrying munitions for dumping it seems likely that someone was not telling the truth.  Shes a great dive with lots to see and I was more than happy to put my training into practice over a few days and explore her.I worked up my experience and gradually introduced my camera to the tec diving realm too.  Photography at any depth is a challenge but below 40m with the extra equipment and processes that the dive alone requires its even more so. With all this wonderful tech diving on my doorstep, I rarely passed up an opportunity and was soon signing up for the Trimix Course and a visit to the infamous USS Lagarto.

Wow – what a dive ! My photographs were included in DIVE Magazines 100 Essential Wreck Dives and I was invited to write about my experience for, amongst others, Scuba Diver Austral-Asia too. There are many more wrecks out there and I still want to dive and photograph the infamous Tottori Maru.  I have dived her – twice now – but I never take my camera in on the first dive of a wreck. I use it more as a scouting dive and circumstances have always conspired against me ever making that second dive…. She just doesn’t want to be photographed but what a wreck!  She was a WWII Hellship used for transporting prisoners.

  Three torpedoes courtesy of the USS Hammerhead took her to her watery grave, thankfully devoid of captives .  She lies on her starboard side and is the epitome  of what a wreck dive should be.  Her stern is fully intact and porcelain peeps out of the sand and silt everywhere you look.  From close to the wheel house the massive damage wrought by the devastating torpedos has twisted the metal like it was no more than a can of coke.  The bow is twisted out and stands almost vertical and glassware can be seen half buried in the silt of the forward compartments.  Oh to get my camera onto the wreck !   The Seacrest Drill Ship is another monster dive.  She went down in Hurricane Gaye amid a whole load of controversy that still rages to this day.  She lies almost upside down and you enter the wreck through the moon pool on the hull.  A veritable wreck divers playground – this is not one for the faint-hearted. Hurricane Gaye wreaked havoc everywhere in this region and one of its much much shallower and easier to access victims lies just a few minutes from Master Divers in Mae Haad Bay in the front of Sensi Paradise Resort. 

This small wreck is perfect for snorkeling and great for families with kids too and it already has its own blog post with pictures and video too.  However Koh Tao still didn’t have its own, dive-able, closer to home wreck.

There was some excitement when in 2009 a tiny dive boat succumbed to the weather and sank.  She was moved to just outside of Japanese Gardens for all to enjoy.Being wooden she very quickly attracted life and growth and her yellow colour was quickly cloaked.  She wasn’t very big though and one of the ferries would moor up to her.  Soon she was dragged into the channel and lost, probably broken up and never to be seen again.
So that spelt the end of wreck diving until the aforementioned wreck pioneers decided the MV Trident has served her dues and it was time that she made her final voyage to the great scrap heap in the sky… Or maybe not?  Wouldn’t it be fitting that the vessel that cruised the waters looking for wrecks became a wreck herself.The Save Koh Tao Group took ownership of the project and many dive schools donated money. A huge fund raising event was organised  and the money was raised for her purchase and stripping.  She was laid to rest in Sept 2010 close to Shark Island amongst local controversy.

Some felt that they had been duped into giving money to support a wreck project that was too deep for Open Water Divers to enjoy. In reality she was always planned to be deep so that she has something to offer both more experienced divers and training tech divers too.

She’s certainly great for a 30% Nitrox dive, the Deep Diver Course and also for Tec 40 and Tec 45 too and those that fancy something a little different to colourful reef dives. She sits slightly askew and is home to large schools of fish already.  She is in quite a currenty area so it is essential to check the tide charts and plan your dive accordingly. Which brings us nicely to the present day when the Thai Navy donated the HTMS Sattakut to Koh Tao diving.  Regular readers will know I have written many blogs about this exiting event  – starting with the first time we saw her back in June this year.  Bad weather hampered the sinking but we were there to document her final moments afloat.  

The bad weather caused the vessel to not only not sink where planned but also to fall over on her side.  A lot of time and effort was then spent in July trying to right and move her to to where she should’ve been.  Clearly the wreck itself never got the memo because as soon as she was upright and a handful dived her, she slipped back over again. Not to be beaten, the team involved once again stood her up and here she has remained.  She now lies extremely close to Hin Pee Wee.  In my mind too close – just a few fin kicks from the bow- which has added pressure to Hin Pee Wee, rather than relieving pressure – which is a definite goal of any artificial reef.   But you cant please all of the people all of the time and she is a great dive.

She’s certainly a lot of fun, with her bow and deck guns still intact shes a perfect first tour of a wreck for any diver and great for the Wreck Adventure Dive on the Advanced Course her depth makes her great for Nitrox too.

The penetration is free of the usual hazards making it great fun for the already trained and perfect for those practicing their skills on the Wreck Course too.  We do go quite often and its just 10 mins on the longtail from the beach too which makes it a perfect nip-out-and-dive site.  You can see more pictures from our visits on our Daily Diving Reports.  Check out the 18th Aug when we dived Chumphon and the HTMS Sattakut (Whoa !) and then again on the 25th Aug too.   More recently we have produced a video tour of the inside and outside of her – you can see it here.


So there you have it a not-so-short history of  wrecks around Koh Tao.  Whatever your level if you love the metal then its here!


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Quick Sketch of the HTMS Sattakut

Since its sinking in mid June, we have visited the HTMS Sattakut quite frequently – its a short 10 min hop on our longtail and perfect to visit at any time.  The wreck has been consistently cloaked in a thermocline  so far but thermoclines are clearing in deeper water already. Maybe it will clear here too or it could just be, as some suggestwe will see this clear – only time will tell.  Dive Master Phill made this quick sketch for briefing purposes and we thought we would share it with you.Life has moved in already and snappers are seen scooting around the hull.  Spider crabs have been spotted trying to hide and yesterday we saw a type of sea hare that we have never seen here before.  We believe they are the  Bursatella leachi, commonly called the ragged or shaggy sea hare. Unfortunately I did not have my camera with me but you can see an example here.

(Don’t forget to sign up to the RSS feed, top left, to keep up to date or you can bookmark the Daily Diving Page to check out the conditions in the underwater world here on Koh Tao!)

If you enjoyed this page, don’t forget to LIKE it just beneath!